agronomy Article An Appraisal of Calcium Cyanamide as Alternative N Source for Spring-Summer and Fall Season Curly Endive Crops: Effects on Crop Performance, NUE and Functional Quality Components Leo Sabatino 1,* , Giovanni Iapichino 1,*, Salvatore La Bella 1, Teresa Tuttolomondo 1, Fabio D’Anna 1, Mariateresa Cardarelli 2 , Beppe Benedetto Consentino 1 and Youssef Rouphael 3 1 Department of Agricultural, Food and Forest Sciences, University of Palermo, 90128 Palermo, Italy; [email protected] (S.L.B.); [email protected] (T.T.); [email protected] (F.D.); [email protected] (B.B.C.) 2 Consiglio per la Ricerca in Agricoltura e L’analisi Dell’economia Agraria, Centro di Ricerca Orticoltura e Florovivaismo, 84098 Pontecagnano Faiano, Italy; [email protected] 3 Department of Agricultural Sciences, University of Naples Federico II, 80055 Portici, Italy; [email protected] * Correspondence: [email protected] (L.S.); [email protected] (G.I.); Tel.: +39-091-23862252 (L.S.); +39-091-23862215 (G.I.) Received: 28 July 2020; Accepted: 7 September 2020; Published: 10 September 2020 Abstract: A two-year study was conducted in both spring-summer and fall seasons to evaluate calcium cyanamide (CaCN2) as an alternative nitrogen (N) source for curly endive (Cichorium endivia L. var. crispum) grown in a Mediterranean environment. Four types of N applications were administered: 1 (i) pre-transplanting base application of 100 kg N ha− corresponding to 100% of the supplied N 1 (100CC), (ii) pre-transplanting base application of 50 kg N ha− corresponding to 50% of the supplied 1 N (50CC) complemented with 50 kg N ha− as ammonium nitrate (50AN) supplied through fertigation, 1 (iii) standard application of 100 kg N ha− as ammonium nitrate (100AN) supplied entirely through 1 fertigation, and (iv) a N-deprived control (0 kg N ha− ) used as base reference to calculate the N use efficiency indices (NUE). Fall season increased head fresh weight, head height, stem diameter and plant visual quality, compared with the spring-summer season. The CaCN2 and standard fertigation N applications were equally effective in increasing head fresh weight and other physical parameters such as, head height, stem diameter, visual quality, number of leaves and head dry matter when compared to the unfertilized control. However, in spring-summer season, CaCN2, especially when 1 applied straight at 100 kg N ha− , effectively increased ascorbic acid and total phenolic content, whereas, in fall season, an increase in TSS and ascorbic acid was recorded. In both, spring-summer and fall seasons, CaCN2 significantly decreased N content and nitrogen accumulation (Nacc). Furthermore, CaCN2 pre-transplant application improved NUE indices both in terms of N fertilizer recovery efficiency and in terms of physiological efficiency of applied N. Our results finally demonstrated that NUE indices increased in the fall season as compared to the spring-summer season. Keywords: Cichorium endivia L. var. crispum; leafy green vegetables; cultivation season; nitrogen fertilizer; CaCN2; functional properties Agronomy 2020, 10, 1357; doi:10.3390/agronomy10091357 www.mdpi.com/journal/agronomy Agronomy 2020, 10, 1357 2 of 13 1. Introduction Curly endive (Cichorium endivia L. var. crispum) is a leafy green vegetable belonging to the Asteraceae family, native to the eastern Mediterranean region and probably originated from the cross between C. intybus and C. pumilum [1,2]. Curly endive is an extensively grown vegetable in Europe and is praised for its typical crunchy texture and slightly bitter taste, rendering it suitable for direct consumption or as an ingredient of mixed ready-to-eat salads. Besides, curly endive is attractive due to its significant amount of nutritional and nutraceutical compounds such as minerals, ascorbic acid, phenolics, glucosinolates and sesquiterpene lactones [3–5]. Nitrogen above-optimal fertilization of vegetable crops represents a potential risk for human health. In particular, due to its accumulation in the edible part of leafy vegetables, NO3− is considered an anti-nutrient [6,7] and therefore a cut back of its dietary consumption is suggested as a precautionary health care action. We assume that curly endive, although less cultivated than other leafy vegetables, is equally prone to NO3− accumulation in the leaves when subjected to above-optimal nitrogen fertilization. Various authors reported that calcium cyanamide (CaCN2) might be used as a soil fumigant for managing soil-borne diseases [8], pests and viruses in the soil [9], or as a tool to impede soil acidification, and expand yield and the quality of fruits [10,11]. However, CaCN2 is also a well-recognized nitrogen fertilizer, particularly in the vegetable crop sector, and it may represent a valuable alternative to traditional soluble fertilizers. It may also improve the crop NUE [12] through a better modulation of N supply [13]. Several researches have demonstrated that nitrogen use efficiency (NUE) and NO3− accumulation are affected by numerous interrelated factors such as fertilization rate and source, irrigation type, and growing season [14–20]. CaCN2 application represents an easy, efficient and practical technique for leafy green vegetables fertilization. However, to our knowledge, there are no reports concerning the relationship between growing season and CaCN2 fertilization doses for curly endive. Thus, the scope of our research was to assess the effects of various CaCN2 pre-transplanting applications on yield, NUE, nutritional and functional traits of curly endive grown in spring-summer and fall seasons. 2. Materials and Methods 2.1. Plant Material, Growing Conditions and Treatments The experiments were conducted in open field in two successive cropping seasons, spring-summer and autumn 2018 and repeated in 2019 at the Experimental Farm of the Department of Agricultural, Food and Forest Sciences of Palermo (SAAF), Sicily (Italy). Meteorological data were collected by the meteorological station of SAAF. Maximal and minimal daily temperature and rainfall in the course of the plant growth cycles were registered (Figures1 and2). On 3 May and on 24 September 2018, curly endive (Cichorium endivia L., var. crispum Hegi) (var. Trusty, HM Clause, France) plug plants at the four-five true leaves stage were transplanted at 2 a density of 10 plants m− . The soil of the experimental field was a Typic Rhodoxeralf soil made of sand, silt and clay with a percentage of 46.5, 22.3 and 31.2, respectively, and a pH of 7.2, highly rich in exchangeable K2O, phosphorous, total nitrogen and organic matter with the following concentrations 1 of 660 ppm, 68 ppm, 2% and 3.1%, respectively. Two doses of CaCN2 at 100 kg N ha− (100CC) or 1 at 50 kg N ha− (50CC) were applied by broadcasting on the whole plot surface and subsequently 1 1 incorporating into the soil (10 cm depth) 505.0 kg ha− or 252.5 kg ha− , respectively of granular CaCN2 (19.8% of N) (Perlka; AlzChem, Trostberg, Germany). CaCN2 was applied 15 days before transplant. 1 The pre-transplant implementation treatment of 100 kg N ha− (100CC) (100% of the supplied nitrogen) 1 was compared with the treatment including a pre-transplant implementation of 50 kg N ha− (50CC) 1 (50% of the supplied nitrogen) by adding to the latter an implementation of 50 kg N ha− (50AN) 1 supplied in the form of NH4NO3 (26% of N) by fertigation (192.3 kg ha− NH4NO3). These two treatments were compared with a treatment including a conventional implementation of 100 kg N 1 1 ha− (100AN) supplied in the form of NH4NO3 (26% of N) by fertigation (384.6 kg ha− NH4NO3). Drip irrigation was applied to all plots as per standard grower practice and in order to avoid plant Agronomy 2020, 10, 1357 3 of 13 water stress. Two growing seasons (spring-summer vs. autumn) were combined with the four Agronomy 2020, 10, x FOR PEER REVIEW 3 of 12 fertilizationAgronomy 2020 rates, 10,(Table x FOR PEER1) in REVIEW a two factorial experimental design accounting for a total3 ofof 12 eight treatments. Each treatment was made of three replicates with 10 plants per replicate and 240 plants treatment was made of three replicates with 10 plants per replicate and 240 plants overall. The overall.treatment The experiment was made wasof three repeated replicates in 2019 with in 10 the plants same per growing replicate period. and 240 plants overall. The experiment was repeated in 2019 in the same growing period. experiment was repeated in 2019 in the same growing period. 45 45 Rainfall (mm) - 2018 Rainfall (mm) - 20182019 14 40 Rainfall (mm) - 2019 14 40 Minimum temperature (°C) - 2018 MinimumMaximum temperattemperatureure (°C)(°C) -- 20182018 MaximumMinimum temperattemperatureure (°C)(°C) -- 20192018 12 35 12 35 MinimumMaximum temperattemperatureure (°C)(°C) -- 20192019 Maximum temperature (°C) - 2019 30 10 30 10 25 25 8 8 20 20 6 Temperature (°C) Temperature 6 Temperature (°C) Temperature 15 Rainfall (mm) 15 Rainfall (mm) 4 10 4 10 2 5 2 5 0 0 0 0 2 July 5 July 8 July 3 May 6 May 9 May 5 June 8 June 11 July 14 July 12 May 15 May 18 May 21 May 24 May 27 May 30 May 02 June 11 June 14 June 17 June 20 June 23 June 26 June 29 June 2 July 5 July 8 July 3 May 6 May 9 May 5 June 8 June 11 July 14 July 12 May 15 May 18 May 21 May 24 May 27 May 30 May 02 June 11 June 14 June 17 June 20 June 23 June 26 June 29 June Figure 1. Daily minimum and maximum air temperature and rainfall at Marsala, Trapani province FigureFigure 1. Daily 1. Daily minimum minimum and and maximum maximum airair temperaturetemperature and and rainfall rainfall at atMarsala, Marsala, Trapani Trapani province province (longitude 12°26′ E, latitude 37°47′ N, altitude 37 m) during the spring-summer growing season (2018 (longitude(longitude 12◦26 12°260 E,′latitude E, latitude 37 37°47◦470 N,′ N,altitude altitude 37 m) m) during during the the sp spring-summerring-summer growing growing season season (2018(2018 and 2019).